This invention relates in general to Roots type supercharger and, more specifically, to improvements in reliability and operation of Roots type superchargers through improvements in gas seals between rotors and the adjacent casing and end plates.
Internal combustion engines have long used superchargers of one type or another to get more air into the engine to permit more fuel to be burned and increase engine power output. A variety of superchargers have been developed, including vane type, turbochargers and Roots type superchargers.
Roots type superchargers have come into widespread use with racing automobiles, motorcycles, boats and the like because of their high efficiency and reliability. In its simplest form, a Roots type supercharger consists of two elongated rotors, each shaped like a FIG. 8 in cross section, running between end plates in an oval-shaped casing, on parallel shafts and geared together so that the rotor lobes are always in near-contact along a line. Clearances between the rotors and between rotors and the casing and end plates are kept to a minimum but with no direct contact. As the rotors rotate they collect air from an inlet in the casing carry it around the outside and direct it to an outlet at higher pressure. The inlet side is a considerably lower pressure than the outlet side.
The space between the outer edge of the rotors and the casing surrounding the rotors and between the ends of the rotors and the casing end plates adjacent to the rotor ends must be kept at a minimum to prevent excessive gas leakage therethrough, which would reduce supercharger performance. Contact must be avoided to prevent wear on the rotors or casing or other damage such as scoring which would increase gas leakage. Gases easily pass between excessively spaced surfaces which provide a smooth walled, uniform width, gas passage. Attempts to add surface seal materials, such as Teflon fluorocarbon strips, at these locations have been largely ineffective due to the difficulty of securing the strips in place and rapid wear due to the wiping action of the seals.
Thus, there is a continuing need for improvements in Roots type superchargers to overcome this gas leakage and sealing problem.